An open-jaw flight arrives in one city and departs from another. It can suit a one-direction multi-city route, but only after you compare the fare, ground transport, airport access, and extra lodging as one trip.
Map the route before the fare
An open-jaw ticket is useful when returning to the arrival city would add a long backtrack. Start with the places you want to connect, then test which airports make the route coherent.
Price the complete journey
Include the transfer to the departure airport, baggage, taxes, and any night required before the return flight. A cheaper ticket can still create a more expensive trip.
Keep the final connection resilient
Avoid placing a long ground transfer immediately before an important flight when alternatives exist. Check current schedules and cancellation conditions for each leg.
Read Is an open-jaw flight worth it for a multi-city trip? or build a plan.